Swipe to dismiss in Android Kotlin - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens when you swipe an item in a RecyclerView with ItemTouchHelper?

Consider a RecyclerView with an ItemTouchHelper attached to enable swipe to dismiss. What is the expected behavior when the user swipes an item fully to the left?

A The item changes color but remains visible in the list.

B Nothing happens; the swipe gesture is ignored.

C The app crashes due to missing swipe callback implementation.

D The item is removed from the adapter and disappears from the list.

💡 Hint

Think about what swipe to dismiss means for a list item.

Swiping an item fully triggers the removal callback, which removes the item from the adapter and updates the UI to hide it.

❓ lifecycle

intermediate

When should you update your data source after a swipe to dismiss?

In a swipe to dismiss implementation, when is the best time to update the underlying data source to remove the swiped item?

A Immediately inside the onSwiped callback before notifying the adapter.

B After the RecyclerView animation finishes, using a delayed handler.

C Never update the data source; just hide the item visually.

D Only when the user confirms the deletion via a dialog.

💡 Hint

Consider the role of onSwiped callback in ItemTouchHelper.

The onSwiped callback is designed to notify you when an item is swiped. You should update your data source immediately there and notify the adapter to keep UI and data in sync.

🔧 Debug

advanced

Why does the app crash with IndexOutOfBoundsException after swipe to dismiss?

You implemented swipe to dismiss but after swiping an item, the app crashes with IndexOutOfBoundsException. What is the most likely cause?

Android Kotlin

override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
  dataList.removeAt(viewHolder.adapterPosition)
  recyclerView.adapter?.notifyItemRemoved(viewHolder.adapterPosition)
}

A The dataList is not synchronized with the adapter's data causing mismatch.

B You must call notifyDataSetChanged() instead of notifyItemRemoved().

C The adapterPosition changes after removal; notifyItemRemoved should use the old position before removal.

D You forgot to override getItemCount() in the adapter.

💡 Hint

Think about how dataList and adapter data relate.

If the dataList used in onSwiped is not the same list the adapter uses, removing from it causes mismatch and crashes. The adapter and data source must be consistent.

🧠 Conceptual

advanced

How does ItemTouchHelper.Callback control swipe directions?

In ItemTouchHelper.Callback, which method controls the allowed swipe directions for items?

A onSwiped() sets the swipe direction dynamically at runtime.

B onMove() returns the swipe direction as a boolean.

C getMovementFlags() returns flags indicating allowed drag and swipe directions.

D getSwipeDirs() is a method to disable swipe gestures.

💡 Hint

Look for the method that returns flags for movement.

getMovementFlags() returns a combination of drag and swipe directions as flags. This controls which gestures are enabled for each item.

❓ navigation

expert

What is the best way to restore a swiped item after dismissal?

After implementing swipe to dismiss, you want to allow users to undo the dismissal by restoring the item. Which approach is best?

A Immediately restore the item in onSwiped without removing it from the data source.

B Show a Snackbar with an Undo button that reinserts the item into the data and notifies the adapter.

C Reload the entire RecyclerView adapter data from the database on undo.

D Disable swipe to dismiss and use a long press to delete instead.

💡 Hint

Think about user experience and minimal UI disruption.

Showing a Snackbar with Undo is a common pattern. It lets users reverse the removal easily without reloading all data.

Practice

1.

What is the main purpose of implementing onSwiped in ItemTouchHelper.SimpleCallback when using swipe to dismiss?

easy

A. To change the background color of the list item

B. To add a new item to the list

C. To disable swipe gestures on the list

D. To remove the swiped item from the data and update the UI

Solution

1. Step 1: Understand the role of onSwiped

   This method is called when a user swipes an item. It is used to handle what happens after the swipe gesture.

2. Step 2: Identify the correct action after swipe

   The typical action is to remove the swiped item from the data source and notify the adapter to update the UI.

3. Final Answer:

   To remove the swiped item from the data and update the UI -> Option D

4. Quick Check:

   onSwiped removes item [OK]

Hint: Remember: swipe means remove item and refresh list [OK]

Common Mistakes:

• Trying to add items in onSwiped
• Ignoring data update after swipe
• Using onSwiped to change colors only

2.

Which of the following is the correct way to create a SimpleCallback for swipe to dismiss only (no drag) in Kotlin?

val callback = object : ItemTouchHelper.SimpleCallback(?, ?) {}

easy

A. 0, ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT

B. ItemTouchHelper.UP or ItemTouchHelper.DOWN, ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT

C. ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT, 0

D. ItemTouchHelper.UP or ItemTouchHelper.DOWN, 0

Solution

1. Step 1: Understand SimpleCallback constructor parameters

   The first parameter is for drag directions, the second for swipe directions.

2. Step 2: Set drag to 0 and swipe to left or right

   For swipe to dismiss only, drag should be 0 and swipe should allow left or right.

3. Final Answer:

   0, ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT -> Option A

4. Quick Check:

   Drag=0, Swipe=LEFT|RIGHT [OK]

Hint: Drag=0 disables drag; swipe=LEFT|RIGHT enables swipe [OK]

Common Mistakes:

• Swapping drag and swipe parameters
• Using drag directions when only swipe needed
• Setting swipe to 0 disables swipe

3.

Given this code snippet inside onSwiped:

val position = viewHolder.adapterPosition
items.removeAt(position)
adapter.notifyItemRemoved(position)

What will happen when the user swipes an item?

medium

A. The item remains but the UI flashes

B. The item is removed from the list and the UI updates to reflect the change

C. The app crashes due to invalid position

D. Nothing happens because notifyItemRemoved is missing

Solution

1. Step 1: Remove item from data list

   The code removes the item at the swiped position from the data list.

2. Step 2: Notify adapter about removal

   Calling notifyItemRemoved updates the UI to remove the item visually.

3. Final Answer:

   The item is removed from the list and the UI updates to reflect the change -> Option B

4. Quick Check:

   Remove item + notify adapter = UI updates [OK]

Hint: Remove data then notify adapter to update UI [OK]

Common Mistakes:

• Not removing item from data list
• Forgetting to notify adapter
• Using wrong adapter position

4.

What is wrong with this onSwiped implementation?

override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
    adapter.notifyItemRemoved(viewHolder.adapterPosition)
    items.removeAt(viewHolder.adapterPosition)
}

medium

A. The adapter position is not valid inside onSwiped

B. The method is missing a call to super.onSwiped

C. Calling notifyItemRemoved before removing item causes UI inconsistency

D. Nothing is wrong; this code works fine

Solution

1. Step 1: Check order of operations

   notifyItemRemoved should be called after removing the item from the data list.

2. Step 2: Understand impact of wrong order

   Calling notifyItemRemoved first causes the adapter to update UI before data changes, leading to inconsistency or crash.

3. Final Answer:

   Calling notifyItemRemoved before removing item causes UI inconsistency -> Option C

4. Quick Check:

   Remove data first, then notify adapter [OK]

Hint: Always update data before notifying adapter [OK]

Common Mistakes:

• Not removing item before notify
• Calling super.onSwiped unnecessarily
• Using wrong adapter position

5.

You want to implement swipe to dismiss in a RecyclerView but only allow swipe to the right. Which code snippet correctly sets up the SimpleCallback and handles the swipe?

val callback = object : ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.RIGHT) {
    override fun onMove(...) = false
    override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
        val pos = viewHolder.adapterPosition
        items.removeAt(pos)
        adapter.notifyItemRemoved(pos)
    }
}
ItemTouchHelper(callback).attachToRecyclerView(recyclerView)

hard

A. This code allows swipe only to the right and removes the item correctly

B. This code allows swipe both left and right

C. This code will crash because onMove is not implemented properly

D. This code does not remove the item from the list

Solution

1. Step 1: Check swipe directions in SimpleCallback

   Swipe is set to ItemTouchHelper.RIGHT only, so only right swipe is allowed.

2. Step 2: Verify onSwiped removes item and notifies adapter

   onSwiped removes the item at adapterPosition and calls notifyItemRemoved correctly.

3. Step 3: Confirm onMove returns false

   Returning false disables drag, which is intended here.

4. Final Answer:

   This code allows swipe only to the right and removes the item correctly -> Option A

5. Quick Check:

   Swipe=RIGHT only + remove item + notify adapter [OK]

Hint: Set swipe directions and remove item in onSwiped [OK]

Common Mistakes:

• Setting swipe to LEFT or both directions
• Not removing item from data list
• Returning true in onMove causing drag